Wayland is a display server which was (at the time of writing) introduced as
the default display server in GNOME. It is said that Wayland will eventually
replace X11 as the default display server on Linux and many distributions
have begun implementation of Wayland. Wayland is a more modern display
server and has a smaller code base currently. Wayland is still under
development, and there are still applications and behaviours that don’t work
as expected, you may find that some applications have not been updated to
work properly in Wayland and currently the only way these applications will
run is using Xorg instead of Wayland. This includes some legacy system
applications and games.

Wayland is enabled by default in the GNOME Desktop. You can choose to run
GNOME in X11 by choosing the Gnome on xorg option in the session chooser on
the login screen. Currently KDE still uses X11 and although there is a
plasma-wayland session available, it is not considered stable or bugfree at
this time.

One way to determine if you’re running in Wayland, is to check the value of
the variable $WAYLAND_DISPLAY. To do this type:

If you are not running under Wayland the variable will not contain any
values. You can also use loginctl to show you what tpe of session is
running:

To determine your session number, simply typing loginctl should provide
your session details.

There is also a legacy X11 server provided with Wayland for compatibility
purposes. To determine what applications are running in this mode, you can
run the following command:

There is also the lg (looking glass) tool in GNOME that will allow you to
determine what display server a window is using. To do this, you run the
application by typing lg in the run dialog or at the command line, select
“Windows” in the upper right corner of the tool, and click on the
application name (or open window) you want to know about. If the window is
running in wayland it will say “MetaWindowWayland” and if it is running in
X11 it will say “MetaWindowX11”.

To find out more about Wayland, please see the following website:

https://wayland.freedesktop.org/

If you need to determine if an issue you are experiencing is related to
wayland, see the Fedora wiki at the link below:

https://fedoraproject.org/wiki/How_to_debug_Wayland_problems